Reciprocating diaphragm pump with packless piston-cylinder unit

ABSTRACT

This invention provides a sealing mechanism for sealing the piston-cylinder unit of a reciprocating diaphragm pump to ensure that the piston-cylinder unit is permanently and reliably sealed while being simple to assemble. The invention further provides a piston-cylinder unit which has almost no play in the micrometer (μm) range, and which is sealed by hydrodynamically sealing a slot thereof.

BACKGROUND

1.0 Field Of The Invention

This invention relates generally to reciprocating diaphragm pumps, andmore particularly to the sealing of the dosing piston/cylinder unit of areciprocating diaphragm pump.

2.0 Discussion Of Related Art

The dosing precision of reciprocating diaphragm pumps depends on theexactness with which the dosing piston is sealed in the associatedcylinder unit. The use of mechanical sealing elements, for exampleO-rings, has the disadvantage that when the sealing elements wear,dosing accuracy is reduced. In addition, it is often very difficult andexpensive to maintain the narrow tolerances essential for adequateprecision at the assembly stage.

European patent EP-B-0 129 187 describes a reciprocating diaphragm pumpwith pre-delivery. In this pump, the dosing piston is actuated via aslidably mounted drive piston. The product to be delivered or dosed isfed to the dosing piston by means of a membrane. The dosingpiston/cylinder unit sealed by O-rings as the sealing element. Thesystem of dosing piston, sealing elements and stroke adjustment screw issubject to wear and limits the useful life. The more stringent therequirements which dosing precision has to satisfy, the shorter the timea system such as this can be used without readjustment or replacement ofthe sealing elements.

SUMMARY OF THE INVENTION

An object of the present invention is to ensure simple assembly andguarantee exact sealing of the dosing piston/cylinder unit of areciprocating diaphragm pump.

In a one embodiment of the invention, a sealing system of the pumpincludes a dosing piston/cylinder unit that is substantially free fromplay in the micrometer range and is sealed by a hydrodynamic gap seal.

In another embodiment of the invention, a reciprocating diaphragm pumpincludes a dosing piston guided with minimized play, i.e. with atolerance in the μm range, in that both part of the cylinder which formsthe compression zone, and the gap remaining between the dosing pistonand the cylinder are sealed by a hydrodynamic gap seal which seals bymeans of the product taken in by the pump. The hydrodynamic gap sealworks without wearing and, accordingly, provides for virtually unlimiteduseful life in regard to the sealing of the system.

In a preferred embodiment of the invention, the dosing piston and thecylinder are made of oxide ceramic. The fact that the dosingpiston/cylinder is made of oxide ceramic has the particular advantagethat these elements can readily be manufactured to the narrowesttolerances.

In another embodiment of the sealing system and the reciprocatingdiaphragm pump, the dosing piston is floatingly actuated via a couplingand, in the reciprocating diaphragm pump, the dosing piston isfloatingly connected by a coupling to a drive piston. The floatingactuation of the dosing piston via a coupling provides for simpleassembly and enables the dosing piston/cylinder unit to operate withhigh reliability.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in more detail in the following withreference to the sole FIGURE of the accompanying drawing.

DETAILED DESCRIPTION OF THE INVENTION

In the reciprocating diaphragm pump illustrated in the drawing, a drivewith a drive piston 5 projects laterally into the reciprocatingdiaphragm pump. Between two pump housing parts 12, 13, a diaphragm 6 issealingly arranged in a circle in an inner pump chamber 14. Thediaphragm 6 is tightly clamped at its periphery and allows the drivepiston 5 to make a reciprocating movement in its directions of movementindicated by a double arrow. In the direction away from the inner pumpchamber 14, the drive piston 5 with the diaphragm 6 arranged thereonmakes a lifting or suction movement (suction stroke); in the directiontowards the inner pump chamber 14, it makes a compression movement(pumping stroke).

In the middle of the reciprocating diaphragm pump, a dosing piston 1 anda cylinder 2 are disposed as a co-operating pair of elements inside theinner pump chamber 14. The dosing piston 1 and the cylinder 2 form adosing piston/cylinder unit 16. The dosing piston 1 is connected to thedrive piston 5 by a coupling 4 so that the lifting and compressionmovements of the drive piston coupling 5 are transmitted to the dosingpiston 1. A control bore 8 extends through the cylinder 2. A dosingopening 11—opposite the diaphragm 6—of the reciprocating diaphragm pumpis actuated by a control valve 9. In addition, the reciprocatingdiaphragm pump comprises a suction valve 7 and a return pressure valve10 on opposite sides of the inner pump chamber 14. The gap 3 between thedosing piston 1 and the cylinder 2 is hydrodynamically sealed by theliquid product situated in the inner pump chamber 14, and in acompression chamber 15. In this part of the cylinder 2 forming thecompression chamber 15, the dosing piston 1 is guided substantially freefrom play with a tolerance in the μm (micrometer) range.

The reciprocating diaphragm pump operates as follows: when the diaphragm6 moved by the drive piston 5 moves away from the inner pump chamber 14(suction stroke), product is taken in through the suction valve 7 and avacuum or reduced pressure is created in the compression chamber 15 ofthe dosing piston/cylinder unit 16. If, during the corresponding liftingmovement of the dosing piston 1, the control bore 8 in the cylinder 2 isopened, the product pre-delivered into the inner pump chamber 14 by thelifting movement of the diaphragm 6 flows into the compression zone 15.During the compression movement (pumping stroke) of the drive piston 5with the dosing piston 1 towards the dosing opening 11, the control bore8 is closed again. Pressure is applied by the dosing piston 1 to theliquid then enclosed in the compression chamber 15 with the result thatthe pressure valve 9 opens and liquid product is dosed through thedosing opening 11. At the same time, excess product is returned via thereturn pressure valve 10 to an intake container operatively connected tothe reciprocating diaphragm pump, the return pressure valve 10 openingunder the effect of the pressure applied by the diaphragm 6 to theproduct present in the inner pump chamber 14.

Towards the drive or diaphragm piston 5, the coupling 4 connecting thedosing piston 1 and the drive piston 5 has a shape adapted to thecorresponding end face of the diaphragm piston 6, and for “floatingly”connecting the dosing piston 1 and the drive piston 5 so that even acentral shift, for example, can easily be compensated by assembly andmanufacturing tolerances. This provides for inexpensive manufacturebecause the “floating” connection eliminates the requirement for narrowtolerances.

What is claimed is:
 1. A pump for dispensing an accurate dose of aliquid product, said pump comprising: a pump housing; an inner pumpchamber for receiving and containing a liquid product to be dosed; acylinder contained within the housing; a dosing piston configured forsliding within said cylinder, said piston forming, in combination withsaid cylinder, a compression chamber during a stroke cycle of the dosingpiston; a gap formed between the dosing piston and cylinder, said gapbeing hydrodynamically sealed by the liquid product occupying the innerpump chamber and the compression chamber; a diaphragm connected to saiddosing piston, said diaphragm being in contact with the liquid productin said inner pump chamber; and a control bore formed in the cylinderfor providing a fluid connection between the compression chamber and theinner chamber during a stroke cycle of the dosing piston, for permittingthe liquid product to flow from the inner chamber into the compressionchamber prior to dispensing.
 2. The pump of claim 1, wherein said innerchamber is in fluidic connection with both a supply flow regulator forreceiving liquid product from the latter, and an exit flow regulator forreleasing excess liquid product from said inner chamber to the former,under conditions of vacuum and positive pressure caused by differentstroke cycles of the dosing piston, respectively, within the innerchamber.
 3. The pump of claim 1, further comprising: a dosing openingfor dispensing the liquid product from said compression chamber during astroke cycle of the dosing piston; and a control valve located betweensaid dosing opening and said compression chamber, said control valvebeing configured for permitting the liquid product to exit thecompression chamber under positive pressure, while preventing back flowof the liquid product into the compression chamber under vacuum.
 4. Thepump of claim 1, wherein said dosing piston and said cylinder consist ofoxide ceramic.
 5. The pump of claim 1, further comprising: a drivepiston configured for actuating the sliding movement of the dosingpiston within the cylinder; and a coupling for connecting the drivepiston to the dosing piston, said coupling being further adapted forcompensating for manufacturing tolerances or variations between saiddosing and drive pistons.
 6. The pump of claim 2, wherein said supplyand exit flow regulators are each comprised of at least one check valve.7. The pump of claim 3, wherein the control valve includes a ball checkvalve.